Background <p>In October 2016, precautions of the package inserts for ethical drugs containing statins were revised for immune-mediated necrotizing myopathy (IMNM).</p> Objective <p>Our objective was to assess the trend in statin-associated IMNM reported before and after the release of the revised precautions in Japan.</p> Methods <p>We investigated the number of case reports and estimated annual incidence rate of statin-associated IMNM using the Japanese Adverse Drug Event Report and Japan Medical Data Center (JMDC) databases, respectively. To identify IMNM case reports, we used the preferred term “immune-mediated myositis” (MedDRA version 27.1).</p> Results <p>We identified 172 statin-associated IMNMs in 145 case reports of patients between 1 April 2004 and 31 March 2023. The most common suspected statin administered to the patients was rosuvastatin (34.3%), followed by pitavastatin (25.0%) and atorvastatin (22.1%). No statin-associated IMNM was reported in patients who were treated with combination agents containing statins. The number of reported statin-associated IMNMs increased from 3 in 2015 to a peak of 51 in 2019, after which it was 22 (2020), 17 (2021), and 21 (2022) in the following years. The estimated annual incidence rate did not differ with statins, it rarely exceeded 5 per 1,000,000 patients.</p> Conclusions <p>There was an increasing trend in the number of statin-associated IMNM after the revised precautions of package inserts for statins were released.</p>